You’re at the pump, and consider refueling with premium gas. It’s only a few cents more per gallon, and it must be better for your vehicle, right? A recent AAA study found that changing the octane of your fuel actually doesn’t help the vehicle if the manufacturer doesn’t suggest doing so. If regular gasoline (usually 87 octane) is recommended for your car, using a higher octane will not lead to any added benefits—you’d simply be wasting money, and spending a few more cents per gallon adds up. In fact, AAA has estimated that Americans waste $2.1 billion a year buying high-octane fuel when it isn't recommended by manufacturer.

It is worth noting that increasingly, modern vehicles are requiring higher-octane fuel to improve performance and efficiency. AAA's study only examined vehicles that do not call for premium gasoline. If your vehicle manufacturer advises using mid-grade or premium fuel, it is best to follow that recommendation.

Separate AAA research on annual driving costs from 2017 suggests that fuel is the second most expensive aspect of owning a vehicle, with the average car owner spending $1,500 on gasoline per year.

Premium vs. Top Tier

"Regular," "mid-grade," and "premium" refer to a gasoline's octane rating, which isn't an indictator of its quality or energy content. Rather, it measures the gasoline's compression ability—high-compression engines can squeeze high-octane fuel harder without igniting it too early, or "knocking."

Top Tier gasoline, on the other hand, contains detergents that help keep "gunk" from building up in the engine. In that sense, it's a higher-quality gasoline. Read more about Top Tier gas.

Since fuel grade and fuel quality are separate, it's possible to find regular-grade Top Tier gas, as well as premium-grade non-Top Tier gas.

Results of AAA's octane study

The fuel octane study compared what happened to vehicles of the same make and model when fueled by premium versus regular gasoline. The factors analyzed were horsepower, fuel economy, and tailpipe emissions—all tested in a lab under various driving conditions.

There were no significant differences in any of the tests, indicating that using premium gasoline when it wasn't required or recommended offers no improvement in engine power, engine efficiency, or engine cleanliness.

Who uses premium, & who actually needs premium?

How many drivers are buying unnecessary high-octane fuel? Despite the fact that the vast majority of vehicles only need regular, AAA found that about 16.5 million U.S. drivers used premium fuel unnecessarily in the last 12 months. Most of those drivers used premium at least once a month.

70% of drivers

in the U.S. own a vehicle that only requires regular-grade gas

16% of drivers

in the U.S. own a vehicle that recommends premium-grade gas

10% of drivers

in the U.S. own a vehicle that recommends mid-grade gas

4% of drivers

in the U.S. own a vehicle that uses an alternative fuel source

"What if my car recommends premium, but doesn't require it?"

Some cars recommend using premium gas, but don't require it, raising an obvious question: Does using premium fuel in those vehicles make them perform better? AAA performed tests to find out. See the results.

The takeaway for drivers

The percentage of vehicles that use mid-grade or premium fuel has been growing and is expected to continue to do so as manufacturers work to keep up with fuel economy standards. Unless you're driving one of those cars, though, you won’t be doing your engine any favors by filling up with a higher octane fuel.

It's important to note that the results of this research don't apply to vehicles that recommend mid-grade or premium fuel, and drivers of such vehicles should not switch to regular gas.

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